1. Field of the Invention
The invention relates to mufflers with a deep-drawn inner shell and a deep-drawn housing shell.
2. Description of the Prior Art
In U.S. Pat. No. 4,396,090, an exhaust gas muffler is disclosed that has an inner shell consisting of two sheet metal plates laid one atop the other. The sheet metal plates of the inner shell are deep-drawn in such a manner that an S-shaped exhaust duct is created which is perforated at various locations. Furthermore, there is a housing shell, which likewise consists of two deep-drawn sheet metal plates laid one atop the other. The housing shell is placed onto the inner shell in such a manner that chambers are created between the inner shell and the housing shell. Finally, there is a partitioning wall of drawn sheet metal, which is clamped into the housing shell and holds the inner shell. The inner shell and the housing shell each have a flange, and the flanges are connected to one another in a gas-tight manner by a single welded seam.
In DE-A-22 28 700, a muffler is disclosed for opposed-cylinder engines arranged at the rear end of a vehicle. The housing consists of two deep-drawn shell halves with an encircling flange. A separating wall divides the housing interior into two chambers. The housing shell halves and the separating wall are connected by suitable connection means, e.g., by a welded seam. In order to allow exhaust gas to be conducted and sound to be muffled, the partitioning wall has openings as well as built-in and mounted parts which form absorption chambers, expansion chambers and reflection chambers as well as Venturi nozzles.
In U.S. Pat. Nos. 4,132,286; 4,415,059; 4,865,154; and 5,012,891, further mufflers are disclosed which consist of a deep-drawn inner shell and a deep-drawn housing shell which are laid one atop the other in such a manner that all four sheet metal plates can be connected to one another in a gas-tight manner with a single encircling welded seam in the area of the flanges. In the housing shell, deep and roughly V-shaped transverse folds are drawn, which touch the inner shell over the entire housing breadth and thus provide the same effect as the separate partitioning walls of the muffler previously described, albeit at twice the material expense.
In all of these mufflers, the flanges of the inner shell and those of the housing shell are connected to one another via a single, encircling weld seam, as mentioned. This can lead to mechanical problems, because the sheet metal plates of the inner shell, which are in direct contact with the hot engine exhaust gases, heat up and expand to a considerably greater extent than the sheet metal plates of the housing shell, which are externally cooled by the driving wind. Furthermore, a welded seam, due to the heating associated with it, leads to change in the microstructure of the sheet metal material, resulting under certain circumstances in intensified corrosion.
In GB-A-1 012 463, mufflers are disclosed with a deep-drawn inner shell and a deep-drawn housing shell, the flanges of which are connected to one another not in a material-bonded manner by means of welded seams, but rather in a positive-locking manner by means of a lock seam. In practice, however, lock-seam connections for four sheet metal plates laid one atop the other can be manufactured only at great expense, whereby the necessary imperviousness entails additional difficulties. The described muffler also has a partitioning wall, for which purpose the sheet metal plates of the inner shell are cut out and bent accordingly.
Finally, GB-A-632 013 discloses a muffler with a deep-drawn inner shell and a deep-drawn housing shell, the flanges of which are laid one atop the other. The flange of the housing shell, however, is broader than that of the inner shell, so that upon mechanical connection by means of lock seam only the sheet metal plates of the housing shell are deformed. The flange of the inner shell is clamped between the non-deformed parts of the flange of the housing shell.
In the last-mentioned design, the flanges of the inner shell and the housing shell are not connected to one another in a non-detachable fashion across their full length, so that in purely theoretical terms the possibility exists of relieving thermal stresses between the inner shell and the housing shell. However, due to the large contact area between the two flanges, there are considerable holding forces at work and compensating movements can scarcely be expected. In addition, the gap which the clamped-in inner shell causes between the sheet metal plates of the outer shell leads to production and corrosion problems. The correct centering of the inner and outer shells is also problematic in this design, since given the closed housing a position check is no longer possible.